Process of tanning



Patented. Dec- 19371 I Arthur J. Green,

A. Lawrence.

Marblehead, Mass assignor to Leather Company, Peabody,

Mass, a corporation of Maine No Drawing. pplication October 1, 183 5, I

' Serial N0. 43,083 Y 11 Claims. .(01. 149-4) The present invention relates to process of tanning.

' which is thick and is penetrated by the vegetable chloride or ammonium sulphate, and then place" The tanning of hides and skins to produce leather ordinarily requires a considerable time for the completion of the process. This is particularly true in the production of sole leather tannins very slowly. The usual practice in the preparation of this type-of leather'is to de-lime the limed hide with lactic acid or ammonium it in the rocker yard for a week or more. A weak or nearly spent vegetable tan ble'nd is used in the first rocker. Each day the hides-are subjected to ,a slightly stronger blend which has been flowed or pressed from the preceding day's work. After twelve, fourteen or twenty-one days in the rocker yard as may be required, withgradually increasing strength of liquors, the hides are placed in the lay away yard with stronger vegetable tan liquors. At times these are fortified by the addition of ground tan bark which is sprinkled between the layers of hides;

at intervals the hides are removed and put in other layers containing still stronger liquors. Thus the hides may receive one, two, three or four layers. During all this period there'has' been a slow and gradual absorption of the vegetable tannins and a combination of ,these tannins with the hide substance. The'wltole process takes as long'as one hundred and twenty days,

and if an increase over the normal degree of tannage is desired, the time must be extended very materially.

' It is the object of the present invention to provide a new and improved process whereby this long time required for the tanning, and particu-' l'arly ofxthe heavier leather such as sole leathe may be greatly shortened, and the degree of tannage increased, thereby, reducing the cost.

Briefly, these objects are accomplished by freezing the hides, either in'untannedor partially tanned condition, under controlled conditions so that the fibre bundles of the hide will-be loosened I and expanded to. facilitate the penetration of the tanning material, but at the same time avoiding the rupturing of. the cells or fibre bundles with a consequent weakening or reduction in the tensile strength of the hide. If large ice crystals are allowed to form in this freezing step, as would be the case if the hides were slowly frozen at a temperature only slightly below freezing point, the cells and fibre bundles would be damaged, resulting in an inferior quality of leather. Where, however, the freezing is controlled-andonly small sized ice crystals-permitted to form. as in the case of so-called quick freezing at temperatures of -30 F. or thereabouts, no appreciable rupturing of the cells or damage to the fibre bundles occurs, and the final product will be a leather having the same life and tensile strength as if it had never been subjected to freezing. In certain respects the quality of the leather is even improved due, apparently, to the more rapid, complete, and even distribution of the tanning material throughout the hide structure.

It has been found that untanned hides, subjected to this freezing process, after twelve days v in the rocker yard can be completely tanned in .the lay away yard in twenty days less than the time ordinarily required. Furthermore, by con tinuing the tanning in the lay' away yard, the degree of tannage andthe yield and iron of the leather can be increased in the same time or less than required by the methods now in use.

In the preferred form of the present invention the hides, after the usual soaking, liming,

and unhairing operations, are washed for an hour ina. cold pool at about 68 F. This is merely a bath of pure water. Instead of transferring the hides directly to the rocker yard, as is now .norgnally done, they are removed from the cold pool and subjected to quick freezing at about 30 F. At this time the hides are in a hydrated and swollen condition, and by the quick-freezing and formation of small ice crystals, the bundles of hide fibres are gently opened aged.

After freezing, the. hides are thawed by immersion in a water bath at or around room temperature and are then carried through the usual subsequent operations, such .as de-liming or bating, and thenthe treatment in the rocker yard yard and it is here the greater saving in time is secured, the opening up or distension of the fibre ."bundles by the ice crystals'in the freezing step leaving them still open and distended after thawing so that the tanning liquid penetrates the hide substance more easily and completely and evenly to effect the tanning operation.

While ordinarily-it is preferred to subject the hide in untanned' condition to the freezing temperature immediately on its removal. from the cold pool, it may be desirable to freeze at some out without being ruptured or otherwise damother stage in the complete process. For example,

the hide may be frozen during the liming process,

or after bating, or even after part of the rocker 40 following the rocker yard comes the lay away yard process, that is, after partial tannage has taken place. Nor is the present invention limited to vegetable tanning as it may be employed with chromium, aluminum, tungsten, and other tannages.

The advantages which result from the reduction in the time required for the tanning operation are obvious. Not only are inventories of hides and liquors reduced, but also the amount of equipment required. Furthermore, the leather may be tanned and put on the market quicker than with the present process, and hence losses due to fluctuation in the market may be avoided. Where it is necessary to curtail production, large amounts of tanning liquor would not be left idle to deteriorate from oxidation, fermentation, etc.,

with heavy loss to the tanner.. In the present process the volume of liquors required is greately reduced and any such losses from deterioration following a curtailment of production would be correspondingly decreased.

Furthermore, the degree of tannage can be easily increased and'the yield or iron of leather raised over that possible in the same period by the present methods, merely by continuing the treatment in the lay away yard. Thus, by the present process the same quality of leather may be secured with a substantial saving in time and equipment, or an improved quality may be obtained at no greater expense.

Having thus described the invention, what is claimed is: I

1. The method of tanning hides and skins which comprises subjecting the untanned hydrated and swollen hide or skin to quick freezing and thereafter thawing the hide and subjecting it to the action of the tanning material.

2. The method of tanning hides and skins which comprises subjecting the untanned hydrated and swollen hide or skin to quick freezing and thereafter subjecting the frozen hide or skin to a solution containing tanning material to thaw and tan the hide.

3. The method of tanning hides and skins which comprises subjecting the untanned hydrate'd and swollen hide or skin to a temperature hide, and thereafter thawing the skin and subiecting it to the action of tanning materials.

' 4. The method of tanning hides and skins which comprises subjecting the hide or skin to the action of tanning material, thereafter quick freezing the hydrated and swollen hide, and then thawingthe frozen hide and subjecting it to .which consists in quick freezing the hydrated and swollen hide before the tanning is completed.

' 6..Thatstep in the tanning of hides and skins which comprises the quick freezing of the untanned hide or skin at a temperature of approximately -30 F.

7. That step in the tanning of hides and. skins which comprises the quick freezing of the hide or skin at a temperature of approximately 30 F. preliminary to the tanning operation.

8. That method of expediting the tanning of hides and skins without substantially reducing their tensile strength, which comprises subjecting the hydrated and swollen hide or skin to quick freezing prior to the completion of the tanning operation.

9. The method of treating untanned hides and skins to expedite the tanning operation, which consists in freezing the hide or skin at a temperature of approximately -30 F. to loosen and open the fibre structure of the hide without substantially reducing its tensile strength.

10. The method of treating untanned hides and skins which consists in-soaking and liming the hide or skin, and thereafter quick freezing the hide or skin while in hydrated and swollen conning material without substantially reducing the tensile strength of the hide.

11.'The method of treating untanned hides and skins which consists in soaking and liming the hide or-skln, quick freezing the hide or skin while in hydrated and swollen condition, and thereafter subjecting the frozen hide or skin to the action of tanning'mate'rial at a temperature above the freezing point.

ARTHUR J. GREEN. 

